Various conventional oscillator structures are known.
As a first example, conventional ring oscillators are known that can include a ring of logic circuit elements.
As a second example, conventional oscillator circuits are known that can include a capacitor that is charged or discharged in conjunction with dual differential amplifiers. One differential amplifier can detect a high threshold level for the capacitor and charge down (discharge) the capacitor when the threshold is exceeded. Conversely, the other differential amplifier can detect a low threshold level for the capacitor and can charge up the capacitor when the capacitor voltage falls below this threshold.
While conventional dual differential amplifier approaches can provide an adequate periodic signal source, such approaches can have drawbacks. As is well known, differential amplifier circuits can include a common mode range. Consequently, when two such circuits are employed in an oscillator circuit, such common mode ranges can limit allowable voltage swings on the capacitor. This can present unwanted design/operational constraints on the oscillator circuit.
Conventional oscillator circuits, like those noted above, can have a temperature dependence that is native to the material in which the circuits are formed. Further, conventional approaches have tended to seek a linear, or essentially constant relationship between temperature and oscillating frequency. However, in some applications, such a single temperature coefficient over an entire temperature range may not be sufficient. As but one example, as is well known, dynamic random access memory (DRAM) cells must be periodically refreshed to maintain data values on storage capacitors. However, the rate at which charge can leak from DRAM cells may not vary linearly over temperature. Consequently, timing the refresh of such cells with conventional oscillator circuits may only address leakage rates in a narrow temperature range.
In light of the above, it would be desirable to arrive at an oscillator circuit that can have different responses over different temperature ranges.
In addition, due to the continuing goal of providing integrated circuits that operate at lower power supply voltages, it would be desirable if such an oscillator circuit can operate with a relatively low power supply voltage.